Find My Friends allows you to easily locate friends and family using your iPhone, iPad, or iPod touch. Just install the app and invite friends to share locations by choosing from your contacts or entering their email addresses.

When a friend accepts your invitation using the Find My Friends app on their device, you can start following their location immediately and they can send a quick request to follow your location. If at any time you don’t want to be followed, you can hide your location with a single switch.

Find My Friends lets you set up location-based alerts that can notify you automatically when a friend arrives at the airport, a child leaves school, or a family member arrives home safely. You can also set up alerts to notify friends about changes in your location.

For best location accuracy and notification performance, make sure Wi-Fi is enabled on your device.

Spotlight: Free Full Software

WhatsApp Messenger is the world's most popular instant messaging app for smartphones.

You can use it to send and receive text and voice messages, photos, videos, even call your friends in other countries, and because it uses your phone's internet connection it might not cost you anything at all (depending on whether you'll pay data charges).

It's easy to set up and use. There's no need to create and remember new account names or pins because it works with your phone number, and uses your regular address book to find and connect you with friends who use WhatsApp already.

You can talk one-to-one or in group chats, and because you're always logged in there's no way to miss messages. Even if your phone is turned off, WhatsApp will save your messages and display them as soon as you're back online.

There's plenty more (location sharing, contact exchange, message broadcasting) and the app is free for a year, currently $0.99/ year afterwards.